In French patents FR 2 699 121, FR 2 713 557 and FR 2 713 558 there are descriptions of such a rim. When viewed in meridian section (i.e. in a plane containing the rotation axis), this rim has a first seat with two ends, the axially outer end being closer to the rotation axis than is the axially inner end of the same seat (such a seat being said to be “inclined outwards”), a more or less large bearing area designed to receive a removable support ring, perhaps a mounting groove, and a second rim seat, either identical (inclined outwards) or different from the first rim seat (i.e. inclined inwards).
Each outward-inclined rim seat has a part that forms a flange (positioned axially on the inside of said seat) to balance the axial forces due to the internal inflation pressure of a tire mounted on the rim, and a hump or projection of small height (less than the height of the rim flange) to keep the bead of a tire in place on the seat even when the pressure in the tire is low or zero.
This rim, together with a removable support and a tire with a suitable meridian carcass reinforcement profile and beads of geometry appropriate for making contact with the rim seats, forms a rolling assembly that can continue working even when rolling at low or even zero pressure. Here, ‘working’ means that the tire remains in place on its rim under these particular conditions without coming off the rim (loss of contact between the tire beads and the rim seats) and therefore without risk of losing control of the vehicle equipped with tires of this kind.
Patent EP 1194305 describes a process for demounting such a tire assembly by positioning a demounting insert of triangular section between a bead seat of the tire and a rim seat inclined outwards, the height of said section once in place being close to or greater than the height of the hump (or projection). In this way the bead is brought partly radially outside the hump and can be pushed axially outwards either by a pressure roller acting on the opposite side, or by the action of a lever inserted between said demounting insert and the tire bead.
As stated in that document, the length of the demounting insert must be chosen so as to reconcile at the same time the need to distance the bead radially from its seat so that it can be moved over the hump, and the need not to constrain the bead too much by producing contact pressures between bead and seat that are too large. For that purpose the length must be appropriate (if the length is too large, the excess contact pressure is such that it may become impossible to demount the tire assembly).
It has been found that positioning the demounting insert is a delicate operation requiring sustained attention and possibly needing several attempts, since the insert tends either not to engage in the first place or not to engage over its full length. To position it, a pressure roller is generally used to push one of the beads axially inwards and so make it pivot about its heel (the heel being the part of the bead axially on the inside in contact with a rim flange), so as to produce a space between said bead and the corresponding rim seat. One end of a demounting insert is introduced into that space. Then, by moving the pressure roller over the bead, it is sought to make the entire insert enter between the bead and the rim seat. During this second operation the insert quite often fails to engage correctly and its positioning must then be restarted from the beginning.
The device according to the invention solves this problem.